A CRITIQUE OF ENTROPY AND GRAVITY IN TRAVEL FORECASTING

ENTROPY MAXIMIZATION HAS BEEN EXPLORED IN RECENT LITERATURE AS A THEORETICAL APPROACH TO THE PRINCIPLE OF GRAVITY IN TRAFFIC FORECASTING. IN THIS PAPER IT IS ARGUED THAT IDENTICAL RESULTS CAN BE OBTAINED WITHOUT SUCH METAPHYSICAL METHODS. THE ALTERNATIVE PROPOSED IS UTILITY MAXIMIZATION BY TRAVELERS, WHICH TIES IN NEATLY WITH CONSUMPTION THEORY IN ECONOMICS. THE UTILITY APPROACH, MOREOVER, PROVIDES A MORE GENERAL FRAMEWORK FOR PREDICTION AND EVALUATION AND ALLOWS A UNIFIED APPROACH AT ALL LEVELS OF TRANSPORTATION SYSTEMS ANALYSIS. THE GRAVITY FORMULA IS DERIVED FROM A UTILITY MAXIMIZATION MODEL, WITH DISTANCE ENTERING EITHER AS AN EXPONENTIAL OR POWER FUNCTION. THE DERIVATION ILLUSTRATES THE THEORETICAL LIMITATIONS OF THIS APPROACH. ALSO CONSIDERED IS THE PROBLEM OF AGGREGATION OVER HOUSEHOLDS. THE MODIFICATIONS TO THE FUNCTIONAL FORM THAT ARE REQUIRED TO MEET MORE STRINGENT TESTS OF ECONOMIC THEORY ARE IDENTIFIED.